Ring-shaped packing washers with a circular cross-section, so-called O-rings, are widely used for providing a frictional grip between various parts in various types of valves. These ring-shaped packing washers are economical, they are easy to install, and they generally provide quite satisfactory performance. The conventional way in which this type of packing washer is used to establish a radial hold is by inserting it in a ring-shaped cavity in one of the parts between which the grip or hold is to be established. The dimensions of this cavity, taking into account the play between the parts, are such that the circular cross-section of the O-ring is radially compressed between the bottom of the cavity and the surface. In the axial direction the cavity should be sufficiently deep so that following radial compression, the dimension of the packing washer along the axial direction increases so that its original circular section becomes oval with a smaller diameter in the radial direction than in the axial direction. This arrangement lends itself to establishing a hold or frictional grip between the working parts that are fixed with respect to each other. However, when one wishes to establish a radial hold between relatively mobile parts, this arrangement can give rise to problems if the parts themselves, as the apparatus functions experience a change in their dimensions, for example, because of different thermal expansions. In this case the degree of radial compression of the packing washer is modified and the packing washer which is excessively stressed by an increase in the radial compression may obstruct or impede the relatively displacement between the parts. This becomes a serious problem especially if the force available for displacing a mobile part is limited, as is the case in thermostatically controlled mixing valves, especially on the return run which is driven by a spring whose force is not very high. Problems similar to those caused by thermal expansions may also arise due to variance of the design dimensions of such parts. The problems discussed with relation to the use of an O-ring can also be found in the use of other types of packing washers, such as the so-called quadrings (retaining rings with four lips).
Japanese patent application No. 58-68546 proposes a retaining device consisting of an O-ring for a piston movable in a cylinder where, for the purpose of increasing the service life of the packing washer and increasing its pressure against the surface of the cylinder, an O-ring is inserted in a cavity that holds it axially and whose bottom is spaced away from the O-ring so as to form a ring-shaped chamber and from this chamber runs a duct that empties out upon the surface of the piston head. In this way, the pressure generated by the piston is transmitted to the ring-shaped chamber and forcefully pushes the O-ring against the wall of the cylinder.